The phase behaviour, ionic conductivity, electrochemical stability and diffusion coefficients of mobile components in three organic ionic plastic crystals (OIPCs): triisobutylmethylphosphonium bis(fluorosulphonyl)amide (P1i444FSI), triisobutylmethylphosphonium bis(trifluromethanesulphonyl)amide (P1i444NTf2) and trimethylisobutylphosphonium bis(trifluoromethanesulphonyl)amide (P111i4NTf2) are compared to study the effect of the anions and cations on phase behaviour and dynamics. The FSI-based OIPC shows lower melting point and higher conductivity values most likely because of the higher degree of charge distributions and weaker ion-ion interactions compared to NTf2 anion-based OIPCs. Cyclic voltammetry of electrolytes consisting of these OIPCs with 70 mol% sodium salt incorporated indicates stable sodium plating/stripping behaviour at 70 and 50 °C for all samples. The magnitude of the peak currents, however, are much higher for the FSI-based electrolyte.